Electronic instrumentation of vehicle wheel alignment examination has progressed in stages from the work disclosed by Senften in U.S. Pat. No. 3,782,831 of Jan. 1, 1974 where toe alignment characteristics of steerable wheels was worked out using a light beam sweeping across a reference line or axis and generating a signal when an opposing photosensitive element registered seeing the light beam. At the moment in time the photosensitive element detects the light beam, the potentiometer voltage is fed into a memory device and is the analog of the angular orientation of the wheel relative to the reference line or axis. There then followed the further disclosure of Senften in U.S. Pat. No. 3,892,042 of July 1, 1975 by which electronic means was applied to compensating the presence of wobble or lateral run-out in the vehicle wheel so that the plane of rotation of the wheel could be found for purposes of alignment determination. In this disclosure the sensing means was mounted on the wheel being examined.
The work of others acknowledged the Senften developments, and in the U.S. Pat. No. of Lill 4,097,157 of June 27, 1978 there was disclosed the application of electronics to determining the alignment of steerable vehicle wheels in relation to the axis of rotation of a single non-steerable wheel. The means associated with the non-steerable wheel took the form of a reflective mirror which was merely assumed to be in a fixed position at right angles to the longitudinal axis of the vehicle when mounted on that wheel.
The continuing work of Senften resulted in the disclosure in U.S. Pat. No. 4,126,943 of Nov. 28, 1978 of electronic means applied to correlating the individual alignment of non-steerable vehicle wheels and the steerable wheels so that the thrust effect of the non-steerable wheels could be applied to alignment of the steerable wheels for improved steering and directional control of a vehicle. There was also the disclosure of Florer et al in U.S. Pat. No. 4,095,902 of June 20, 1978 directed to a method and apparatus for measuring toe angles of vehicle steering wheels wherein electronic circuits were utilized for computing angular displacement of each of the front wheels in relation to a thrust line reference determined by the position of the rear wheels of the vehicle.
An automatic wheel alignment instrument controlled by a microprocessor was disclosed by Chang in the IECI 1978 Processings of March 20-22, 1978 in Industrial Applications of Microprocessors. This was a general discussion of the subject in which servo accelerometers were pointed out as useful tools for camber determination of vehicle wheels. It was also pointed out that camber and toe are alignment characteristics perpendicular to each other, and if certain facts are known the run out corrections can be made from only one sensor. The obtaining of the facts was not disclosed.